1. Field of the Invention
This invention relates to trimming potentiometers of the type in which a wiper is movable over a resistive member by rotation of a rotatable member attached to the wiper.
2. Description of the Prior Art
Conventionally, the rotatable member is provided with a slot engageable by a screwdriver or a coin to enable it to be turned for adjustment of the potentiometer. However, the adjustment is relatively coarse, so that great care must be taken in adjusting the potentiometer to a precise value and for many applications the accuracy of adjustment thus obtainable is insufficient.
To overcome this disadvantage, there have been made potentiometers incorporating a worm gear engaged with teeth formed on the periphery of the rotatable member. The potentiometer is adjusted by rotation of the worm gear by a screwdriver or a key. Although a suitable velocity ratio between the worm gear and the rotatable member can be achieved so as to facilitate fine adjustments, such a design of potentiometer increases the cost considerably.
It has also been proposed to tooth the periphery of the rotatable member and to rotate this by a tool having a pinion at its end, the pinion being of smaller diameter than the rotatable member, whereby a step-down gear ratio is established. The end of the tool engages a pivot structure on the body of the potentiometer.
Neither of the known proposals deal with another problem confronting the manufacturer of trimming potentiometers, namely the requirement of users for different adjustment directions. By adjustment direction is meant the direction of presentation of the tool relative to the base plane of the potentiometer, which plane is normally defined by the terminal loads of the potentiometer. Typically, the options of adjustment from the top direction and from a side direction are required, and manufacturers supply worm gear potentiometers with the worm gear in two correspondingly different orientations relative to the terminal leads. This requires each potentiometer to be manufactured in two variants and multiplies stocking and ordering problems.